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Learn how to use the FOREIGN KEY constraint to prevent actions that would destroy links between tables in MySQL. See examples of creating, naming, and dropping FOREIGN KEY constraints on CREATE TABLE and ALTER TABLE statements.
In MySQL, InnoDB and NDB tables support checking of foreign key constraints. Foreign key checking is controlled by the foreign_key_checks variable, which is enabled by default. Typically, you leave this variable enabled during normal operation to enforce referential integrity.
Summary: in this tutorial, you will learn about the MySQL Foreign Key constraint and how to create, drop and disable a foreign key constraint. MySQL Foreign Key Introduction. A foreign key is a column (or set of columns) that establishes a relationship between data in two tables.
This tutorial introduces you to MySQL foreign key constraints and shows you how to manage foreign keys effectively.
MySQL supports foreign keys, which permit cross-referencing related data across tables, and foreign key constraints, which help keep the related data consistent. A foreign key relationship involves a parent table that holds the initial column values, and a child table with column values that reference the parent column values.
17 sie 2017 · Foreign keys and referential constraints allow you to set relationships between tables and modify some of the database engine’s actions. This beginner’s guide explains referential integrity and foreign key use in MySQL.
The FOREIGN KEY constraint is a key used to link two tables together. A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
